In a body system of a vehicle, an ECU (Electro Control Unit) called a Body Control Module (BCM: Body Control Module) controls an I/O (Input/Output) device which is connected to the ECU by a dedicated line. There is a problem in that the number of signal lines increases as the number of control targets increases.
To solve the problem above, Patent Literature 1 discloses a method to control I/O devices by storing a status signal of each I/O device in each multiplex transmission apparatus arranged in each part of a vehicle, and connecting the multiplex transmission apparatus and the BCM by a multiplex transmission line.
Patent Literature 2 discloses a method in which when there is a change in input information from an I/O device, in a communication system that adopted a multiplex transmission apparatus such as the above, the multiplex transmission apparatus transmits the input information that changed to the BCM, thereby a BCM is able to detect the change in input information in a short period of time.